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Can radon be present in well water?
Yes. Radon can dissolve into groundwater as it moves through soil and rock containing naturally occurring uranium. A private well may then bring that radon into a home through the water supply.
For most households, the greater concern is not swallowing small amounts of radon in water. The main concern is radon gas escaping from water into indoor air during showers, laundry, dishwashing, bathing, and other normal household activities.
Milwaukee, WI households connected to a public water supply generally do not face the same private-well testing responsibility. However, properties that use a private well should consider both indoor-air radon and waterborne radon as separate questions.
How does radon in water affect indoor air?
Radon is a radioactive gas that cannot be seen, smelled, or tasted. When well water containing radon enters a building, some of the gas can be released into the air.
The amount added to indoor air depends on several factors, including:
- The radon concentration in the water
- How much water the household uses
- The amount of ventilation
- The size and layout of the home
- Whether water is used in enclosed areas such as bathrooms, basements, or laundry rooms
Showering can release radon more quickly than many other uses because water is broken into droplets and mixed with air. A water test result does not directly tell a household’s indoor-air concentration, but it can help identify whether the well may be contributing to the problem.
Most of the health concern associated with radon comes from breathing it over long periods. Long-term exposure to elevated indoor radon increases the risk of lung cancer, with a particularly serious risk for people who smoke or previously smoked.
Is radon in well water common in Milwaukee?
Radon levels in groundwater vary widely from one well to another. Nearby properties can have different results because wells may draw from different depths, rock formations, or groundwater pathways.
Wisconsin testing has generally found that the highest well-water radon results are more common in parts of the state outside the southern area. That does not mean a private well in or near Milwaukee is automatically free of radon. A broad map or regional pattern cannot predict the result for an individual property.
The only way to know whether radon is present in a particular well is to test the water. Indoor-air testing remains necessary because soil gas entering through a foundation is usually the more significant source of radon in a home.
Should a private well be tested for radon?
A private-well household should consider water testing when:
- Indoor air tests above 4 picocuries per liter
- The home has a private well and no previous water test
- A well has been drilled, repaired, deepened, or substantially altered
- A home is being purchased and the water supply has not been evaluated
- Water is used frequently in enclosed areas with limited ventilation
- An indoor-air result remains elevated after common foundation entry points have been addressed
A high indoor-air result does not prove that the well is the source. Testing the air and water separately helps determine whether the problem is primarily soil gas, water, or both.
For a reliable result, use a laboratory qualified to analyze radon in drinking water. Radon can escape from a poorly collected or improperly handled sample, so collection instructions should be followed precisely. A laboratory or public health office can explain the correct container, timing, storage, and shipping requirements.
What does a water result mean?
Radon in water is commonly reported in picocuries per liter, or pCi/L. This is the same general unit used for radon in indoor air, but the two results should not be compared as if they mean the same thing.
For example, 4 pCi/L in air and 4 pCi/L in water represent different exposure situations. Water concentration must be interpreted in relation to household water use and the amount of radon that may transfer into indoor air.
A commonly used estimate is that 10,000 pCi/L of radon in household water may add approximately 1 pCi/L to indoor air, although actual transfer varies. This estimate is useful for understanding scale, not for replacing indoor-air testing.
There is no simple “safe-looking” result based only on taste, odor, or appearance. Radon does not change the way water looks or smells.
What should happen if radon is found in well water?
The first step is to confirm the result and evaluate the indoor air. If the water result is unexpectedly high, a repeat test may help verify the finding, especially if sample collection conditions were uncertain.
If water treatment is warranted, the system generally needs to treat the water before it is distributed throughout the home. This is called point-of-entry treatment.
Two approaches are commonly used:
- Aeration systems: These mix water with air so radon can be released and vented outdoors. The venting design matters because the system must not discharge concentrated radon into a basement, crawl space, attic, or other occupied area.
- Granular activated carbon systems: These pass water through carbon that captures radon. The carbon can accumulate radioactivity over time, so maintenance, replacement, and disposal require careful planning.
A filter installed only at the kitchen faucet may reduce radon in drinking water at that tap, but it does not address radon released during showers, bathing, laundry, or other whole-house uses. Point-of-use treatment is therefore limited when the concern is indoor-air exposure.
Water treatment also does not correct radon entering through the foundation. If indoor-air testing shows elevated levels, foundation entry points and the home’s ventilation conditions still need to be evaluated.
Are there special considerations for homes in Milwaukee?
Seasonal conditions can affect radon testing and household ventilation. During cold weather, windows and doors stay closed more often, and homes operate under stronger heating-related pressure differences. These conditions can allow soil gas to accumulate indoors.
Basements are also commonly used for storage, laundry, mechanical equipment, or living space. If a well system, pressure tank, or treatment equipment is located below grade, water-related radon and soil-related radon may occur in the same area.
After substantial plumbing work, well repairs, flooding, foundation changes, or installation of a water-treatment system, retesting may be appropriate. A new treatment device can change how radon moves through the water system, but performance should be checked with follow-up testing.
What other well-water tests are needed?
Radon testing should not replace routine private-well testing. Wisconsin guidance commonly recommends testing private wells for bacteria and nitrate at least annually, with additional testing for substances such as arsenic and lead on a periodic basis.
A well can produce clear, good-tasting water and still contain contaminants. Testing should reflect the property’s well construction, land use, age, past results, and any changes in the surrounding area.
The practical approach is to treat radon in water as one part of a broader household safety review: test indoor air, test the well when appropriate, interpret the results together, and verify any treatment with follow-up testing.